The concept of the invention relates to means for improving the utility of charge-transfer-device type analog shift registers, and more particularly to apparatus for correction of charge-transfer-inefficiency induced distortion occurring in charge-transfer-device analog shift registers.
In the use of charge transfer devices as analog shift registers, it is known that data smear of the shift register response occurs. Such data smear or signal distortion is caused by charge transfer inefficiency in the charge transfer device cell, as is well known in the art, such phenomenon being discussed in the following U.S. patents:
U.S. Pat. No. 3,925,806 to Strain et al.
U.S. Pat. No. 3,868,516 to Buss
U.S. Pat. No. 3,946,248 to Buss
U.S. Pat. No. 3,963,942 to Sequin et al.
U.S. Pat No. 3,919,468 to Weimer
Such references also deal variously with means for processing the CCD shift register output to variously overcome limited aspects of the data smear. For example, U.S. Pat. No. 3,925,806 to Strain et al. teaches the use of a static or fixed transversal filter for correction of signal tail smear. In other words, Strain's filter does not employ adaptively weighted gain coefficients.
U.S. Pat. Nos. 3,868,516 and 3,946,248 to Buss variously employ (1) a filter in which the taps or gain weights are modified, (2) a fixed inverse model filter approximation and (3) a regenerator inserted in a delay line to provide a preselected weighting function which is subtracted from a preceding slope output so as to achieve dispersion compensation. However, Buss does not teach the use of adaptive filtering in which the gain weightings are automatically adjusted to effect optimum compensation of signal "tail smear".
U.S. Pat. No. 3,963,942 to Sequin et al. addresses itself to clean-up of a d-c bias, but does not address itself to compensation of signal sample tail smear nor to variations in CCD signal gain. U.S. Pat. No. 3,919,468 to Weimer teaches use of a fixed tap transversal filter, rather than adaptive taps. Nor does such reference address bias compensation or compensation for gain changes.
From a review of the prior art, therefore, it is apparent that the matter of compensation for data smear due to charge transfer inefficiency has been variously approached in only a limited fashion.